The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As the automotive industry continues to focus on light weighting vehicles to meet customer expectations on fuel economy and CAFE (Corporate Average Fuel Economy) requirements, interest in alternative materials including aluminum-intensive vehicle architectures has increased. In “body-in-white” structures, (a stage in which structures have been joined together before coating/painting), joining methods have traditionally relied on resistance-spot welding (e.g., in steel structures). In the case of aluminum-intensive vehicles and other mixed metal joining applications, self-piercing rivet (SPR) technology prevails. SPR technology is represented in FIG. 1, where a rivet is inserted into workpieces by a punch, and the workpieces deform into a die to form a “button.”
One advantage of SPR technology is that it is a high production volume assembly process. Further, it is compatible with adhesive joining, where both the mechanical rivet and adhesive joining methods can be used together. Another advantage of SPR technology is that rivets are available in a wide variety of geometries. However, with SPR technology, high setting forces are often required to fully set the rivet into a stack. As the rivet is driven into the material, the head of the rivet comes in contact with the top material, and the setting force increases as the rivet head contacts the top material. High setting forces result in higher tool wear and maintenance requirements, and also require more robust c-frame structures to withstand the higher setting forces, compromising the sections in which they will fit for production. This is often the case when the top material is a harder material.
In addition to high setting forces, corrosion testing has shown that proud rivet head heights can cause corrosion concerns for certain applications. As shown in FIG. 2, gaps under the head of the rivet allow water and foreign objects to settle under the head, thus increasing corrosion risk. One way to resolve this issue is to reduce the flushness tolerance range, but tighter tolerances result in higher manufacturing costs.
This corrosion issue in joined assemblies using a SPRs and related friction elements/fasteners, among other mechanical joining issues, is addressed by the present disclosure.